Human immunodeficiency virus, type-2 (HIV-2), the West African counterpart of the acquired immunodeficiency syndrome (AIDS) virus, is related to, but is quite distinct from HIV-1. The HIV-2 NIH-Z genome is approximately 9.4 kb long with an env gene of about 2.7 kb which codes for an envelope protein of 856 amino acids. The gpl6O envelope protein is matured into a 120 Kd exterior glycoprotein (gpl2O) and a transmembrane protein of 35 Kd (gp35). The gpl2O and gp35 envelope proteins of HIV-2 NIH-Z show about 32% and 39% homology, respectively, with the human T-lymphotropic virus, type-IIIB (HTLV-IIIB) strain of HIV-1. The chief objectives of this project are (1) to develop a diagnostic antigen for accurately detecting antibodies to HIV-2 in all infected human sera and (2) to use the bacterially-expressed HIV-2 env gene products in some vaccine applications. We have expressed the env gene of the NIH-Z isolate of HIV-2 as five overlapping fragments in E. coli. The env open reading frames (ORFS) were initially expressed as tripartite fusions in between the 12 amino-terminal codons of the lambda cII gene and the lacZ (Beta-galactosidase) gene of E. coli that are under the transcriptional control of the lambda PL promoter of the expression plasmid pWS50. The 0-galactosidase portion of the fusion protein was then deleted at the DNA level by generating in-frame translational stops or translational frame-shift mutations. One of the ORFs spanning the amino acid residues 536 through 705 of the HIV-2 env gene directed the synthesis of a 20 Kd protein that was serologically specific for identifying antibodies to HIV-2. This antigenic protein is produced at levels approximately 5% of the total cellular proteins. -No significant immunological cross-reactivity was observed with HIV-1-positive sera or with normal control sera in immmunoblot assays with a crude preparation of this protein. Work is now in progress on the immunological characterization of the gene products of the remaining four HIV-2 env ORFS.